Use of stream in Delphi (2) Use of tfilestream (file stream) for read and write

Tstream is an abstract base class and cannot directly generate objects. In a specific application, it mainly uses its child classes:
Tfilestream: file stream
Tstringstream: String stream
Tmemorystream: memory stream
Tresourcestream: resource file stream

Thandlestream: it is the parent class of tfilestream and a subclass of tstream.
Tcustommemorystream: it is the parent class of tmemorystream and tresourcestream, and a subclass of tstream.

Common stream-related classes include Treader, twriter, tcompressionstream, and tdecompressionstream.

Here is an example of a file stream:

Procedure tform1.button1click (Sender: tobject); var getstream, setstream: tfilestream; {declare a file stream} getpath, setpath: string; begin getpath: = 'C: \ temp \ get.jpg '; {This file needs to exist} setpath: = 'C: \ temp \ set.jpg '; {This will be automatically created} if not fileexists (getpath) then begin showmessage ('the image file to be tested cannot be found: '+ getpath); exit; end; getstream: = tfilestream. create (getpath, fmopenread or fm1_exclusive); setstream: = tfilestream. create (setpath, fmcreate); {two parameters are required to create a file stream: parameter 1 is the path and parameter 2 is the open mode} getstream. position: = 0; {the stream pointer is moved to the start point, starting from here during replication} setstream. copyfrom (getstream, getstream. size); {copy stream} {copyfrom parameter 2 is the size of the content to be copied; if it is 0, no matter where the pointer is, all content will be copied.} {copyfrom returns the actual number of bytes to be copied.} {the set.jpg file is displayed on the hard disk, just like get.jpg.} {It is actually a copy file, but here we use the file stream to implement} getstream. free; setstream. free; end;

  
 

Tfilestream open mode and sharing mode:

Category	Parameters	Description
Dozen Open Module Type	Fmcreate	Create a file. Open it if it exists.
	Fmopenread	Read-only access
	Fmopenwrite	Write-only open
	Fmopenreadwrite	Read/write open
Total Enjoy Module Type	Fm1_compat	Sharing Mode, compatible with DoS
	Fm1_exclusive	Do not allow others to open in any way
	Fmsharedenywrite	Allow others to open in write-only mode
	Fmsharedenyread	Allow others to open in read-only mode
	Fmsharedenynone	Allow others to open in any way